On Fri, Apr 18, 2014 at 08:53:39PM -0600, Myron Stowe wrote: > The vast majority of platforms are not supplying ACPI _PXM (proximity) > information corresponding to host bridge (PNP0A03/PNP0A08) devices > resulting in sysfs "numa_node" values of -1 (NUMA_NO_NODE) [1]: > # for i in /sys/devices/pci0000\:00/*/numa_node; do cat $i; done | uniq > -1 > > # find /sys/ -name "numa_node" | while read fname; do cat $fname; \ > done | uniq > -1 > > AMD based platforms provide a fall-back for this situation via amd_bus.c. > These platforms snoop out the information by directly reading specific > registers from the Northbridge and caching them via 'alloc_pci_root_info'. > > Later during boot processing when host bridges are discovered - > 'pci_acpi_scan_root' - the kernel looks for their corresponding ACPI _PXM > method - drivers/acpi/numa.c::acpi_get_node(). If the BIOS supplied a > _PXM method then that node (proximity) value is associated. If the BIOS > did not supply a _PXM method *and* the platform is AMD based, the > fall-back cached values obtained directly from the Northbridge are used; > otherwise, "NUMA_NO_NODE" is associated. > > There are a number of issues with this fall-back mechanism the most > notable being that amd_bus.c extracts a 3-bit number from a CPU register > and uses it as the node number. The node numbers used by Linux are > logical and there's no reason they need to be identical to settings in the > CPU registers. So if we have some node information obtained in the normal > way (from _PXM, SLIT, SRAT, etc.) and some from amd_bus.c, there's no > reason to believe they will be compatible. > > This patch warns when this situation occurs: > pci_root PNP0A08:00: [Firmware Bug]: No _PXM; guessing node number 0 > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=72051 > > Signed-off-by: Myron Stowe <myron.stowe@xxxxxxxxxx> > --- > > arch/x86/pci/acpi.c | 6 +++++- > 1 files changed, 5 insertions(+), 1 deletions(-) > > diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c > index 01edac6..80c09ba 100644 > --- a/arch/x86/pci/acpi.c > +++ b/arch/x86/pci/acpi.c > @@ -489,8 +489,12 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root) > } > > node = acpi_get_node(device->handle); > - if (node == NUMA_NO_NODE) > + if (node == NUMA_NO_NODE) { > node = x86_pci_root_bus_node(busnum); > + if (node != NUMA_NO_NODE) > + dev_info(&device->dev, FW_BUG "No _PXM; guessing node number %x\n", Hmm, I'm not really convinced this message is user-friendly enough. Can we be more descriptive here please? -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. -- -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
